Polarizer, method of fabricating the same and liquid crystal display having the same

ABSTRACT

Disclosed are a polarizer, a method for fabricating the same, and a liquid crystal display having the same. The liquid crystal display includes a liquid crystal panel and a polarizer attached to the liquid crystal panel. The polarizer includes a polarizing film, a first support film, and a second support film. The first support film has optical anisotropy and is attached to the polarizing film. The first support film has a first thickness. The second support film is attached to the polarizing film while facing the first support film and has a second thickness, which is greater than the first thickness. The polarizer is fabricated by evaporating a solvent from a solution including polymer resin to form an optical film and then elongating the optical film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/034,382, filed on Feb. 20, 2008, and claims the benefit of andpriority from Korean Patent Application No. 2007-17102, filed on Feb.20, 2007, which are both hereby incorporated by reference for allpurpose as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polarizer, a method of fabricatingthe same, and a liquid crystal display having the same. Moreparticularly, the present invention relates to a polarizer capable ofdisplaying high-quality images, a method of fabricating the same, and aliquid crystal display having the same.

2. Discussion of the Background

Generally, a liquid crystal display (LCD) uses liquid crystals todisplay an image by converting electric signals into visual information.The LCD includes a liquid crystal panel containing liquid crystaltherein and polarizers attached to outer portions of the liquid crystalpanel. A first polarizer may be provided on an upper portion of theliquid crystal panel, and a second polarizer may be provided on a lowerportion of the liquid crystal panel. The two polarizers havetransmission axes, which are perpendicular to each other, and thatlinearly polarize light passing through the polarizers in parallel toeach transmission axis thereof. The LCD transmits or absorbs lightpassing through the liquid crystal panel by using the polarizer, therebydisplaying images.

However, various factors may cause image quality degradation in the LCD.Because there are various factors that may degrade image quality,preventing degradation by analyzing the factors is difficult. Forexample, a “corner Mura” occurs when a corner portion of the image isbrighter than other portions of the image. It is assumed that thepolarizer generates the corner Mura.

SUMMARY OF THE INVENTION

The present invention provides a polarizer that may be capable ofdisplaying high-quality images and preventing the corner Mura.

The present invention also provides a method of fabricating thepolarizer.

The present invention also provides a liquid crystal display includingthe polarizer.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses a polarizer that includes a polarizingfilm, a first support film, and a second support film. The first supportfilm has optical anisotropy and is attached to one side of thepolarizing film. The first support film has a first thickness of 70 μmor less. The second support film is attached to the other side of thepolarizing film while facing the first support film and has a secondthickness, which is greater than the first thickness.

The present invention also discloses a method of forming a polarizerincluding forming a polarizing film, forming a support film havingoptical anisotropy and a first thickness of about 30 μm to about 70 μm,and attaching the support film to the polarizing film. Forming thesupport film includes providing a solution containing polymer resin on astage, forming an optical film by evaporating a solvent from thesolution while moving the stage, and elongating the optical film byrotating a roller, which contacts the optical film, at a speedcorresponding to a moving speed of the stage.

The present invention also discloses a liquid crystal display thatincludes a liquid crystal panel including first and second substratesfacing each other with a liquid crystal layer interposed therebetween. Apolarizer is attached to at least one of the first and secondsubstrates. The polarizer includes a polarizing film, a first supportfilm, and a second support film. The first support film has opticalanisotropy and is attached to one side of the polarizing film. The firstsupport film has a first thickness of 70 μm or less. The second supportfilm is attached to the other side of the polarizing film while facingthe first support film and has a second thickness, which is greater thanthe first thickness.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a sectional view showing a liquid crystal display (LCD)according to an exemplary embodiment of the present invention.

FIG. 2 is an enlarged perspective view of the liquid crystal panel shownin FIG. 1.

FIG. 3A and FIG. 3B are sectional views showing the operation of the LCDshown in FIG. 1.

FIG. 4A and FIG. 4B are views showing axis deviation occurring in aconventional LCD due to difference in shrinkage.

FIG. 5A is a photographic view showing the analysis result for cornerMura occurring in a VA LCD.

FIG. 5B and FIG. 5C are views showing axis deviation, which causescorner Mura, in the Poincare sphere.

FIG. 6 is a graph showing variation of corner Mura in the LCD accordingto thickness of a support film having optical anisotropy.

FIG. 7 is a graph showing variation of the contrast ratio in the LCDaccording to the phase retardation value in the thickness direction of asupport film having optical anisotropy.

FIG. 8A is a photographic view showing graphs that represent variationof image quality according to driving time of a conventional LCD.

FIG. 8B is a photographic view showing graphs that represent variationof image quality according to driving time of an LCD according to anexemplary embodiment of the present invention.

FIG. 9A, FIG. 9B, and FIG. 9C are views showing a fabrication procedurefor a polarizer according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity Like referencenumerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing “on”, “attached to”, or “connected to” another element or layer,it can be directly on, directly attached to, or directly connected tothe other element or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon”, “directly attached to”, or “directly connected to” another elementor layer, there are no intervening elements or layers present.

FIG. 1 is a sectional view showing a liquid crystal display (LCD)according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the LCD includes a liquid crystal panel 100 andpolarizers 200. The liquid crystal panel 100 includes a first substrate110 and a second substrate 120 facing each other. Transparent electrodesare formed on the first and second substrates 110 and 120, respectively.A pixel electrode 115, which is separately aligned according to pixelsthat display the image thereon, is formed on the first substrate 110. Adata voltage corresponding to image information is applied to the pixelelectrode 115. A common electrode 125, which is integrally formedregardless of the pixels, is formed on the second substrate 120. Aconstant reference voltage is applied to the common electrode 125. Aliquid crystal layer 130 is interposed between the pixel electrode 115and the common electrode 125.

The polarizers 200 are attached to outer portions of the liquid crystaldisplay panel 100. Specifically, a first polarizer 210 is attached to anouter portion of the first substrate 110, and a second polarizer 220 isattached to an outer portion of the second substrate 120. The firstpolarizer 210 includes a first support film 211, a first polarizing film212, a second support film 213, and a first adhesive layer 214. Thesecond polarizer 220 includes a third support film 221, a secondpolarizing film 222, a fourth support film 223, and a second adhesivelayer 224. The components of the first polarizer 210 are alignedsymmetrically to the components of the second polarizer 220 about theliquid crystal panel 100.

The first and second polarizing films 212 and 222 polarize light in apredetermined direction, and they include optical films containing polyvinyl alcohol (PVA) compounds. The optical film absorbs iodine (I) ordichromatic dye to be elongated in one direction. Thus, an absorptionaxis is formed along the elongation direction of the optical film, sothat the optical film can absorb light parallel to the absorption axis.

The first and second support films 211 and 213 face each other about thefirst polarizing film 212 so as to support the first polarizing film212. The second support film 213 is thinner than the first support film211. The third and fourth support films 221 and 223 face each otherabout the second polarizing film 222 so as to support the secondpolarizing film 222. The fourth support film 223 is thinner than thethird support film 221. In detail, the first and third support films 211and 221 may be about 80 μm thick to effectively support the first andsecond polarizing films 212 and 222, respectively. In contrast, thesecond and fourth support films 213 and 223 may be about 70 μm thick orless. The second and fourth support films 213 and 223 are thinnerbecause they serve to improve the image quality of the LCD as well as tosupport the polarizing films 212 and 222, respectively. The role of thesecond and fourth support films 213 and 223 in improving the imagequality of the LCD will be described below.

A protective film may be formed on the exposed surface of the thirdsupport film 221, or the exposed surface can be treated. For example,the third support film 221 may be subject to anti-static (A/S) treatmentby using conductive particles. In this case, static electricity may beprevented from being introduced into the liquid crystal panel 100, sothat the LCD may be prevented from malfunctioning. In addition, thethird support film 221 may be subject to anti glare (A/G) treatment byforming corrugation on the surface of the third support film 221. Inthis case, external light may be prevented from being reflected in thefront direction from the surface of the third support film 221, therebypreventing glare.

The first adhesive layer 214 is positioned between the first substrate110 and the second support film 213 to couple the first polarizer 210 tothe liquid crystal panel 100. The second adhesive layer 224 ispositioned between the second substrate 120 and the fourth support film223 to couple the second polarizer 220 to the liquid crystal panel 100.The first and second polarizers 210 and 220, which are attached usingthe first and second adhesive layers 214 and 224, can be detached fromthe liquid crystal panel 100, if necessary. For instance, if thepolarizer 200 has a defect, the polarizer 200 may be detached from theliquid crystal panel 100, and the liquid crystal panel 100 may bereused.

FIG. 2 is an enlarged perspective view of the liquid crystal panel 100shown in FIG. 1.

Referring to FIG. 2, gate lines 111 and data lines 112 are formed on thefirst substrate 110. The gate lines 111 cross the data lines 112 and areinsulated from the data lines 112, thereby defining a plurality of pixelareas (PAs). A thin film transistor 113 and a pixel electrode 115 areprovided in each pixel area PA. The thin film transistor 113 includes acontrol electrode connected to the gate line 111, an input electrodeconnected to the data line 112, and an output electrode facing the inputelectrode and connected to the pixel electrode 115.

A common electrode 125 is formed on the second substrate 120 to face thepixel electrode 115. A light blocking layer pattern may be formedbetween the second substrate 120 and the common electrode 125. The lightblocking layer pattern is positioned corresponding to the gate lines 111and the data lines 112 to block the light on the boundary of the pixelarea PA. A color filter may be formed on the light blocking layerpattern to display a color image.

The operation of the LCD having the above structure will be describedbelow.

FIG. 3A and FIG. 3B are sectional views showing the operation of the LCDshown in FIG. 1.

Referring to FIG. 2 and FIG. 3A, the LCD is converted into a black stateand a white state according to the electric field applied to the liquidcrystal layer 130. With a vertical alignment (VA) mode LCD, the liquidcrystal 131 contained in the liquid crystal layer 130 is alignedperpendicularly to the first and second substrates 110 and 120 when anelectric field is not applied to the liquid crystal layer 130. At thisalignment, the LCD is converted into the black state by means of thefirst and second polarizing films 212 and 222 having transmission axesperpendicular to each other. The liquid crystal 131 alignment directionis defined according to the long-axis direction of the liquid crystal131.

Since the liquid crystal 131 is non-emissive, the LCD typically includesa light emitting unit to provide light used to display an image.Alternatively, the LCD may display an image using light incident fromthe exterior. The light emitting unit supplies light from behind theliquid crystal panel 100, so that light may pass through the firstpolarizer 210, the liquid crystal panel 100, and the second polarizer220. Light incident from the exterior passes through the secondpolarizer 220 and then is reflected from the liquid crystal panel 100.Then, the light is output to the exterior through the second polarizer220. In this type of LCD, the first polarizer 210 can be omitted.

The operation of an LCD including a light emitting unit will bedescribed below. For the purpose of convenience, first and seconddirections D1 and D2 refer to two directions that define a plane surfaceperpendicular to the traveling direction of the light, and the travelingdirection of the light is referred to as a third direction D3. The firstpolarizing film 212 has a first transmission axis 212 a, which isparallel to the first direction D1, and the second polarizing film 222has a second transmission axis 222 a, which is parallel to the seconddirection D2.

The light supplied from the light emitting unit is linearly polarized inthe first direction D1 while passing through the first polarizer 210.The linearly polarized light is incident into the second polarizer 220after passing through the liquid crystal layer 130. Then, the incidentlight is absorbed in the second polarizer 210 having the secondtransmission axis 222 a extending in the second direction D2, which isperpendicular to the first direction D1, so the LCD becomes the blackstate.

Referring to FIG. 2 and FIG. 3B, in the white state of the LCD, a gatesignal and a data signal are transmitted to the gate line 111 and dataline 112, respectively. The thin film transistor 113 is turned on by thegate signal, so that a data voltage corresponding to the data signal isapplied to the pixel electrode 115. At the same time, a common voltagehaving a constant value is applied to the common electrode 125. Thedifference between the data voltage and the common voltage applies anelectric field to the liquid crystal layer 130. In the case of a VA modeLCD, the liquid crystal 131 has negative dielectric anisotropy, so thatthe liquid crystal 131 tends to align perpendicularly to the electricfield. Therefore, the electric field tilts the liquid crystal 131relative to the first and second substrates 110 and 120.

In this state, light supplied from the light emitting unit may belinearly polarized while passing through the first polarizer 210. Thelinearly polarized light then passes through the liquid crystal layer130. Here, the liquid crystal 131, which is tilted relative to thesubstrates 110 and 120, changes the polarization direction of the light.The light having the changed polarization direction includes componentsthat are parallel to the second direction D2. The light components thatare parallel to the second direction D2 pass through the secondpolarizer 220. As a result, the LCD becomes the white state. Thebrightness of the LCD may be proportional to the intensity of theelectric field.

Contrast ratio refers to a ratio between the lowest gray scale blackstate and the highest gray scale white state. If the contrast ratioincreases, high-quality images may be displayed. But the contrast ratiomay be reduced at the lateral side of the LCD, so that the image qualitymay be degraded at the lateral side of the LCD.

A compensation film may be used to improve the image quality at thelateral side of the LCD. The compensation film is provided in at leastone of the first and second polarizers 210 and 220.

According to the present exemplary embodiment, the second and fourthsupporting films 213 and 223 may serve as the compensation films. Thecompensation films are classified into various optical films accordingto components thereof, and the optical films are subject to theelongation process when fabricating the compensation films.

The optical film may be elongated in one direction or two directionsduring the elongation process. The optical film has optical anisotropythrough the elongation process. The optical film's opticalcharacteristics are determined according to the elongation direction andelongation degree of the optical film.

If the refractive index of the optical film is N1, N2, and N3 in thefirst, second, and third directions D1, D2, and D3, respectively, theoptical film has refractive index anisotropy, except when N1, N2, and N3equal each other. Due to this refractive index anisotropy, phaseretardation difference may occur between components of light passingthrough the optical film, thereby changing the light's polarizationdirection. In the following description, phase retardation with respectto the surface defined in the first and second directions D1 and D2 willbe referred to as “phase retardation in the surface direction”, andphase retardation in the third direction D3 will be referred to as“phase retardation in the thickness direction.”

In detail, if the thickness of the optical film is “d”, the phaseretardation value in the surface direction Ro and the phase retardationvalue in the thickness direction Rth are defined as follows.

Ro=|N1−N2|×d

Rth=|(N1+N2)/2−N3|×d

In the LCD, the phase retardation value in the surface direction Ro isrelated to phase variation of light incident in the front direction ofthe LCD, and the phase retardation value in the thickness direction Rthis related to phase variation of light incident in the lateral directionof the LCD. Thus, the compensation film adjusts the phase retardationvalue in the thickness direction Rth to improve the image quality in thelateral direction of the LCD.

Optical films including Cyclo Olefin Polymer (COP) or Tri AcetateCellulose (TAC) compound may be used as the compensation film. Since theCOP-based optical film may have superior strength, it may besufficiently elongated so that it may have an acceptable phaseretardation value in the thickness direction. In contrast, the TAC-basedoptical film has hydrophilic characteristics, so that it may be easilybonded to the polarizing film.

As described above, since the COP-based optical film and the TAC-basedoptical film have their own advantages, and one or both of the COP-basedoptical film and the TAC-based optical film can be used according toapplications thereof. For example, the COP-based optical film may beused for the second support film 213, and the TAC-based optical film maybe used for the fourth support film 223. Additionally, either COP-basedoptical films or TAC-based optical films may be used for both the secondand fourth support films 213 and 223.

The TAC-based optical film may have superior endurance, so that it maybe used for the first and third support films 211 and 221. However,components of the TAC-based optical film used for optical compensationare different from components of the TAC-based optical film used forsupport. In detail, the TAC-based optical film used for opticalcompensation may include a Cellulose Diacetate Propionate compoundexpressed by chemical formula 1, and the TAC-based optical film used forsupport may include a Tri Acetate Cellulose compound expressed bychemical formula 2.

The Cellulose Diacetate Propionate compound may be obtained by replacingone acetate of TAC with a Propionate group. In addition to thedifference in compositions, the TAC-based optical film that is used foroptical compensation is different from the TAC-based optical film thatis used for support in that the TAC-based optical film that is used foroptical compensation is subject to the elongation process duringfabrication.

In the first polarizer 210, the second support film 213, which is usedfor optical compensation, is thinner than the first support film 211,which is used for support. Additionally, in the second polarizer 220,the fourth support film 223, which is used for optical compensation, isthinner than the third support film 221, which is used for support. Ifthe second and fourth support films 213 and 223 are thinner than thefirst and third support films 211 and 221, the corner Mura may beprevented and image quality of the LCD may be improved.

FIG. 4A and FIG. 4B are views showing axis deviation occurring in aconventional LCD due to differences in shrinkage.

Referring to FIG. 4A, in the polarizer of a conventional LCD, apolarizing film 1 is attached to a compensation film 2 while facing eachother. The polarizing film 1 and the compensation film 2 have opticalaxes 1 a and 2 a, respectively. The optical axes 1 a and 2 a correspondto the elongation direction of the polarizing film 1 and thecompensation film 2. In addition, the optical axis 1 a of the polarizingfilm 1 matches with the optical axis 2 a of the compensation film 2.

Referring to FIG. 4B, various external influences are exerted upon theLCD when the LCD is fabricated or used. For example, the LCD may betested by applying heat to a chamber while driving the LCD for apredetermined period of time. In this case, heat is transferred to thepolarizing film 1 and the compensation film 2 provided in the polarizerduring the test process. Since the polarizing film 1 and thecompensation film 2 are fabricated through the elongation process, ifheat is applied to the polarizing film 1 and the compensation film 2,the elongated parts may shrink and return to their initial state.However, they do not shrink uniformly. For instance, when the polarizingfilm 1 has a rectangular shape, the shrinkage of the polarizing film 1along its long side differs from that along its short side, therebycausing the optical axis 1 a of the polarizing film 1 a to deviate fromits initial position. Such shrinkage may similarly occur in thecompensation film 2, so that the film's optical axis 2 a deviates fromits initial position. Since the material of the polarizing film 1differs from the material of the compensation film 2, the polarizingfilm 1 shrinks at a different degree than the compensation film 2. As aresult, as shown in FIG. 4B, the optical axis 1 a of the polarizing film1 is not parallel to the optical axis 2 a of the compensation film 2. Inother words, the optical axis 1 a of the polarizing film 1 may deviatefrom the optical axis 2 a of the compensation film 2. The degree ofdeviation increases at the corner of the films rather than the center ofthe films. Due to the deviation between the optical axis 1 a and theoptical axis 2 a at the corner of the films, degradation of imagequality, by corner Mura, may occur. Such axis deviation may be analyzedby using the Poincare sphere.

FIG. 5A is a photographic view showing the analysis result for cornerMura occurring in a VA LCD.

Referring to FIG. 5A, in the black state, light leakage occurs at eachcorner of the LCD, causing the corner Mura. The degree of light leakagediffers depending on the positions in the pixel area. That is, in the VALCD, the pixel area is divided into a plurality of domains according tothe alignment direction of the liquid crystal, and the domainscompensate for each other to improve the LCD's operationalcharacteristics. As shown in FIG. 5A, the upper domain is brighter thanthe lower domain in the left upper portion and the right lower portionof the LCD. In contrast, the lower domain is brighter than the upperdomain in the left lower portion and the right upper portion of the LCD.

FIG. 5B and FIG. 5C are views showing axis deviation, which causes thecorner Mura, in the Poincare sphere.

Referring to FIG. 5B and FIG. 5C, when three axes S1, S2, and S3 areperpendicular to each other in space, the Poincare sphere satisfies theequation S1 ²+S2 ²+S3 ²=1. Points provided on the surface of thePoincare sphere represent different polarizing states. For instance, allpoints on the equator (S3=0) represent the linear polarized state, andtwo opposite points on the equator represent the linear polarized statesin the opposite directions. In addition, in the Poincare sphere, theArctic (S1=S2=0, S3=1) corresponds to right-handed circular polarizationand the Northern Hemisphere corresponds right-handed oval polarization.In addition, the Antarctic (S1=S2=0, S3=−1) corresponds to left-handedcircular polarization and the Southern Hemisphere correspondsleft-handed oval polarization.

The conventional LCD includes upper and lower polarizers that face eachother with the liquid crystal panel interposed therebetween. The upperand lower polarizers have polarizing films and compensation films,respectively. In this case, light passes through the lower polarizingfilm, the lower compensation film, the liquid crystal layer of theliquid crystal panel, the upper compensation film, and the upperpolarizing film. For the purpose of convenience, optical axes of thelower polarizing film, the lower compensation film, the liquid crystallayer, the upper compensation film, and the upper polarizing film willbe referred to as a first optical axis A1, a second optical axis A2, athird optical axis A3 or A3′, a fourth optical axis A4, and a fifthoptical axis A5, respectively. The first and second optical axes A1 andA2 are assumed that they deviate from the normal state (S1=1, S2=S3=0)in which the axis of the lower polarizer is not distorted, and the thirdand fourth optical axes A3 or A3′ and A4 are assumed that they deviatefrom the normal state (S1=−1, S2=S3=0) in which the axis of the upperpolarizer is not distorted.

Since the alignment direction of liquid crystal varies depending ondomains, the direction of the third optical axis A3 or A3′ of the liquidcrystal layer may vary depending on the domains. That is, in the leftupper and right lower portions of the LCD shown in FIG. 5A, the thirdoptical axis A3 defined by the upper domain is opposite to the thirdoptical axis A3′ defined by the lower domain. Similarly, the opticalaxes in the left lower and right upper portions of the LCD shown in FIG.5A are opposite to the optical axes in the left upper and right lowerportions of the LCD. For instance, the direction of the optical axisdefined by the upper domain in the left upper portion of the LCD may beidentical to that of the third optical axis A3 defined by the lowerdomain in the left lower portion of the LCD, and the direction of theoptical axis defined by the lower domain in the left upper portion ofthe LCD may be identical to that of the third optical axis A3′ definedby the upper domain in the left lower portion of the LCD.

As shown in FIG. 5B, light incident into the lower polarizing film islinearly polarized in parallel to the first optical axis A1 and incorrespondence with the first position P1 on the surface of the Poincaresphere. Light passing through the lower polarizing film passes throughthe lower compensation film so that the light is converted into the ovalpolarized light corresponding to the second position P2. The secondposition P2 is obtained by rotating the first position P1 about thesecond optical axis A2 at an angle corresponding to the phase variationvalue of the light generated from the lower compensation film. Suchposition conversion in the Poincare sphere is also applicable for theliquid crystal layer and the upper compensation film. That is, lightpassing through the upper domain of the liquid crystal layer isconverted into oval polarized light corresponding to the third positionP3. In addition, light passing through the liquid crystal layer passesthrough the upper compensation film, so that the light is converted intooval polarized light corresponding to the fourth position P4.

In the upper polarizing film, the fifth position P5 corresponding to thefifth optical axis A5 represents the brightest white state, and thesixth position P6, which is symmetrical to the fifth position P5,represents the black state. The oval polarized light corresponding tothe fourth position P4 is spaced apart from the sixth position P6, whichshows that light is partially leaked in the black state.

As shown in FIG. 5C, light passing through the lower polarizing film andthe lower compensation film is converted into oval polarized lightcorresponding to the second position P2 while passing through the firstposition P1. In addition, light passing through the lower domain of theliquid crystal layer is converted into the oval polarized lightcorresponding to the third position P3′. Further, light passing throughthe liquid crystal layer is converted into oval polarized lightcorresponding to the fourth position P4′ while passing through the uppercompensation film.

Regarding the interval distance from the sixth position P6 to the fourthposition P4 or P4′, the interval distance in the lower domain is shorterthan the interval distance in the upper domain. That is, the lowerdomain is closer to the black state as compared with the upper domain,and the amount of light leakage in the lower domain is less than that ofthe upper domain. The analysis result using the Poincare sphere based onaxis deviation coincides with the result shown in FIG. 5A. Thus, thecorner Mura is generated due to axis deviation between the polarizingfilm and the compensation film.

Based on the results of the above analysis, exemplary embodiments of thepresent invention minimize axis deviation between the polarizing filmand the compensation film in order to prevent the corner Mura. Forexample, in the exemplary embodiment described with reference to FIG. 1,the second and fourth support films 213 and 223, which serve ascompensation films, are thinner than that the first and third supportfilms 211 and 221, which have the support function. This is because thevariation range of the optical axes of the first and third support films211 and 221 can be reduced as the thickness of the first and thirdsupport films 211 and 221 decreases. In this case, axis deviation of thefirst and third support films 211 and 221 may be minimized when thefilms shrink.

FIG. 6 is a graph showing variation of corner Mura in an LCD accordingto thickness of the support film having optical anisotropy. In FIG. 6,the x-axis is the thickness of the support film and the y-axis is themeasured value of corner Mura. The support film is an opticalanisotropic film including Cellulose Diacetate Propionate. As shown inFIG. 1, the support film is used for both first and second polarizers210 and 220. The corner Mura value is calculated according to thefollowing equation after measuring the brightness in the peripheral areaand the corner Mura area.

Corner Mura value=(Mura area brightness−peripheral areabrightness)/peripheral area brightness

Referring to FIG. 6, the thickness of the support film is linearlyproportional to the corner Mura value. In general, if the support filmhas a thickness in the range of about 40 μm to about 80 μm, the cornerMura value is in the range of about 3 to about 20. Theoretically, if thethickness of the support film is 32.2 μm, the corner Mura is notgenerated. However, a high-quality image can be displayed when thecorner Mura value is about 15 or less.

According to the above-mentioned result, the support film is preferablythin. However, if the support film is too thin, the total thickness ofthe polarizer becomes thin, causing difficulty when removing thepolarizer. For example, when a process fault occurs after attaching thepolarizer to the liquid crystal panel, the polarizer is detached fromthe liquid crystal panel. In this case, a thicker polarizer can be moreeasily detached from the liquid crystal panel. In contrast, if thepolarizer is too thin, the liquid crystal panel may be damaged whendetaching the polarizer from the liquid crystal panel. Thus, taking easeof detachment and corner Mura into consideration, the support filmshould be no more than 70 μm thick. Preferably, the support film has athickness in the range of about 30 μm to about 50 μm.

FIG. 7 is a graph showing variation of the contrast ratio in an LCDaccording to the phase retardation value in the thickness direction ofthe support film having optical anisotropy.

In FIG. 7, the x-axis is the phase retardation value in the thicknessdirection of the support film having optical anisotropy, and the y-axisis the measured contrast ratio. The contrast ratio is obtained from theposition which is inclined from the front side to the lateral side ofthe LCD by an angle of 60°. In addition, the support film is an opticalanisotropic film including Cellulose Diacetate Propionate. As shown inFIG. 1, the support film is used for both first and second polarizers210 and 220.

Referring to FIG. 7, when the phase retardation values in the surfacedirection Ro are 45 nm and 50 nm, the contrast ratio relative to thephase retardation value in the thickness direction Rth at the lateralside is represented in the form of a parabolic curve, which is convexupward. The fault of the image quality is determined on the basis of thepredetermined value (i.e., 40) of the contrast ratio obtained from thelateral side of the LCD. As shown in FIG. 7, the contrast ratio is 40 orless when the phase retardation value in the thickness direction Rth is140 nm or above. Thus, the phase retardation value in the thicknessdirection Rth is preferably set in the range of about 110 nm to about137 nm when the phase retardation value in the surface direction Ro isin the range of about 39 nm to about 53 nm including 45 nm and 50 nm.

FIG. 8A and FIG. 8B are photographic views showing graphs that representvariation of image quality according to driving time of the conventionalLCD and the LCD of the present invention.

Referring to FIG. 8A, when the driving time of the conventional LCD is100 hours or less, brightness is uniform over the whole area of thescreen. However, as the driving time increases, brightness increases atthe corner of the screen, causing corner Mura.

Referring to FIG. 8B, when the thickness of the support film serving asthe compensation film is reduced, brightness is uniformly formed overthe whole area of the screen even if the driving time of the LCDincreases. In this manner, the thinner support film included in thepolarizer can prevent the image quality degradation caused by the cornerMura.

A method of fabricating the polarizer having the support film withreduced thickness will be described below.

FIG. 9A, FIG. 9B, and FIG. 9C are views showing a fabrication procedurefor a polarizer according to an exemplary embodiment of the presentinvention.

Referring to FIG. 9A, a container 10, a stage 20, and a transfer unit 30are prepared. A solution 5 including polymer resin to fabricate thesupport film is contained in the container 10. The polymer resinincludes Cellulose Diacetate Propionate compound. The container 10 isspaced apart from the stage 20, and the solution 5 is discharged ontothe stage 20 from the container 10 through an exhaust port formed at thelower end portion of the container 10. The transfer unit 30 rotateswhile contacting the bottom of the stage 20, thereby moving the stage 20on which the solution 5 is placed.

Referring to FIG. 9B, the stage 20 may move at a constant speed V1 sothat solvent is evaporated from the solution 5. As the solventevaporates from the solution 5, the optical film 6 mainly made ofpolymer resin including Cellulose Diacetate Propionate compound isformed on the stage 20.

Referring to FIG. 9C, the elongation process is performed with respectto the optical film 6. During the elongation process, a pair of rotatingrolls 40 rotate while contacting top and bottom surfaces of the opticalfilm 6. The rotating rolls 40 apply pressure to the optical film 6,thereby elongating the optical film 6. Here, the optical film 6 iselongated in one direction. Although a rotating roller is shown, variouselongation devices can be used if they can elongate the optical film 6.

The rotating speed V2 of the rotating roller 40 corresponds to thetransfer speed V1 of the stage 20. For example, the rotating speed V2may equal the transfer speed V1. In this case, the elongation process isperformed as soon as the optical film 6 is formed, so that thefabrication process can be rapidly performed. In addition, as the speedof the rotating roller 40 increases, greater pressure is applied to theoptical film 6 during the elongation process, so that the thickness ofthe optical film 6 can be easily reduced.

The support film for optical compensation is obtained from the opticalfilm 6 through the elongation process. The support film having thesupport function can be formed without performing the elongationprocess. In the case of the support film having the support function,Tri Acetate Cellulose is used instead of Cellulose Diacetate Propionate.The polarizing film is fabricated separately from the above process byusing poly vinyl alcohol. After that, the support film for opticalcompensation and the support film having the support function areattached to both sides of the polarizing film by a bonding agent,respectively, thereby providing the polarizer.

The polarizer and the LCD having the same according to exemplaryembodiments of the present invention may improve image quality at thefront and lateral sides of the LCD by preventing the corner Mura.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display, comprising: a liquid crystal panelcomprising a first substrate, a second substrate facing the firstsubstrate, and a liquid crystal layer between the first and the secondsubstrates; and a polarizer attached to at least one of the firstsubstrate and the second substrate, wherein the polarizer comprises: apolarizing film; a compensation film attached to one side of thepolarizing film and disposed between the polarizing film and one of thefirst substrate and the second substrate, the compensation film havingoptical anisotropy and biaxial refractive index anisotropy, thecompensation film having a first thickness of 70 μm or less; and asupport film attached to the other side of the polarizing film whilefacing the compensation film.
 2. The liquid crystal display of claim 1,wherein the compensation film comprises a triacetate cellulose compound.3. The liquid crystal display of claim 1, wherein the compensation filmis a cellulose diacetate propionate compound.
 4. The liquid crystaldisplay of claim 1, wherein the compensation film has a phaseretardation value in a surface direction of about 39 nm to about 53 nm,and a phase retardation value in a thickness direction of about 110 nmto about 137 nm.
 5. The liquid crystal display of claim 1, wherein thecompensation film is directly attached to the one side of the polarizingfilm, and the support film is directly attached to the other side of thepolarizing film.
 6. A liquid crystal display, comprising: a liquidcrystal panel comprising a first substrate, a second substrate facingthe first substrate, and a liquid crystal layer between the first andsecond substrates; and a polarizer attached to at least one of the firstsubstrate and the second substrate, wherein the polarizer comprises: apolarizing film; a compensation film attached to one side of thepolarizing film and disposed between the polarizing film and one of thefirst substrate and the second substrate, the compensation film having afirst thickness of 70 μm or less; and a support film attached to theother side of the polarizing film while facing the compensation film,the second thickness being greater than the first thickness.
 7. Theliquid crystal display of claim 6, wherein the compensation filmcomprises a triacetate cellulose compound.
 8. The liquid crystal displayof claim 6, the compensation film is a cellulose diacetate propionatecompound.
 9. The liquid crystal display of claim 6, wherein thecompensation film has a phase retardation value in a surface directionof about 39 nm to about 53 nm, and a phase retardation value in athickness direction of about 110 nm to about 137 nm.
 10. The liquidcrystal display of claim 6, wherein the compensation film is directlyattached to the one side of the polarizing film, and the support film isdirectly attached to the other side of the polarizing film.